Chapter 4Atrial Rhythms

Atrial Dysrhythmias: Mechanisms

Altered automaticity and triggered activity are disorders in impulse formation. Reentry is a disorder in impulse conduction.

Altered Automaticity Altered Automaticity occurs in

normal pacemaker cells and in myocardial working cells that do not normally function as pacemaker sites.

Triggered Activity Triggered Activity results from

abnormal electrical impulses that sometimes occur during repolarization, when cells are normally quiet.

Reentry Reentry (reactivation) is a condition

in which an impulse returns to stimulate tissue that was previously depolarized.› Reentry requires:

A potential condition circuit or circular conduction pathway

A block within part of the circuit Delayed conduction within the remainder of

the circuit

Premature Atrial Complexes (PACs)

A premature atrial complex (PAC) occurs when an irritable site within the atria fires before the next SA node impulse is due to fire.

2 PAC’s

Aberrantly Conducted PACs PACs associated with a wide QRS

complex are called aberrantly conducted PACs.

Aberrantly conducted PACs

Wandering Atrial Pacemaker With this rhythm, the size, shape and

direction of the P waves vary, sometimes from beat to beat.

Notice all of the P waves are different even in the slightest bit.

Multifocal Atrial Tachycardia When the wandering atrial pacemaker

is associated with a ventricular rate greater than 100 bpm, the rhythm is called multifocal atrial tachycardia (MAT).

Atrial Tachycardia An irritable site in the atria fires at a

rate of 150-250 bpm.

Atrial Tachycardia Atrial tachycardia that starts or ends

suddenly is called paroxysmal atrial tachycardia (PAT).

Synchronized Cardioversion Synchronized cardioversion is the

delivery of shock to the heart by means of a defibrillator to terminate rapid dysrhythmia.

AV Nodal Reentrant Tachycardia (AVNRT)

AVNRT is caused by reentry in the area of the AV node.

AVNRT A regular, narrow-QRS tachycardia that

starts or ends suddenly is called paroxysmal supraventricular tachycardia (PSVT).

AV Reentrant Tachycardia (AVRT)

Preexcitation is a term used to describe rhythms that originate from above the ventricles but in which the impulse travels via a pathway other than the AV node & bundle of His

The most common type of preexcitation syndrome is called Wolff-Parkinson-White (WPW) Syndrome.Delta Wave

Atrial Flutter Atrial Flutter is an ectopic rhythm in

which an irritable site fires regularly at a very rapid rate.

Atrial Fibrillation Atrial Fibrillation occurs because of

altered automaticity in one of several rapidly firing sites in the atria or reentry involving one or more circuits in the atria.

These rapid impulses cause the muscles of the atria to quiver (fibrillate).